The present invention relates generally to hybrid inflators useful for inflating air bags and more particularly to a switch for sensing a low pressure condition within the hybrid inflator.
U.S. Pat. No. 4,049,935 is illustrative of one type of pressure switch that may be used in combination with the hybrid inflator which is incorporated herein by reference. The switch of U.S. Pat. No. 4,049,935 is shown in FIG. 1 herein and comprises a pressure vessel 1 sealed at an open end by a diaphragm 2, a pair of reinforcement members 3 and 4 to limit the motion of the diaphragm 2. This pressure switch also includes a switch assembly 5 comprising electrical contacts 6 and 7 and a moveable pin 8. The diaphragm 2 is moveable up and down in relation to the pressure differential acting thereacross. As can be appreciated, the inner surface of the diaphragm is exposed to the pressure of the gas within the pressure vessel 1 of the switch and the outer surface of the diaphragm is exposed to the local environment i.e. the pressure within the hybrid inflator 9 which in and of itself comprises a second pressure vessel filled with pressurized inflation gas. The hybrid inflator is used to inflate an air bag mounted in communication therewith in a known manner. The switch assembly 5 is compressively loaded against other portions of the pressure switch during assembly While not shown in FIG. 1, it can be appreciated that if a mounting bracket end loads (see arrows 11) the pressure switch, this compressive loading will be increased. One deficiency of this type of switch is that the reinforcement members could become bowed because of the compressive loading moving the pin 8 and diaphragm somewhat closer to the contact 6. The closer spacing permitted the pin to prematurely engage the contact 6 forcing same against contact 7 giving rise to a false low pressure signal. FIGS. 2 and 3 further explain this bowing movement using a similar switch arrangement. This switch is end loaded by a support bracket (not shown) to mount the pressure vessel 1 inside the hybrid inflator. The support bracket compressively loads the pressure vessel and switch assembly 5 axially as illustrated by arrows 11 as shown in FIG. 2. As mentioned, this compressive loading may tend to cause the switch assembly to bow upwardly (see FIG. 3) lifting the moveable pin 8. This phenomenon does not occur instantaneously and is time and force dependent causing creep of the plastic parts used in the switch assembly. As can be seen in this bowed configuration, the pin 8 resides closer to the electrical contacts than desirable and occasionally the pressure switch may become inadvertently activated, as the electrical contacts became separated, giving a false indication of a low pressure condition in the hybrid inflator pressure vessel when the pressure was not low.
It is an object of the present invention to provide an improved temperature compensated pressure switch.
Accordingly the invention comprises: a pressure switch adapted to be placed within a pressurized chamber for generating a logical signal when the pressure within the chamber reduces to a determinable pressure P.sup.1. The pressure switch comprises: a pressure vessel sealed at one end by a snap action diagram and having an an inner stop and an outer stop respectively positioned on opposing sides of the diaphragm for limiting diaphragm motion. The outer stop comprises: a first cylindrical portion, a first pair of parallel slots formed therein and a through bore extending therethrough. A switch assembly is loosely mounted to the outer stop. The switch assembly comprises an upper housing member, a lower housing member, first and second electrical contacts and a pin. The upper housing member comprising a hollow cylindrical portion adapted to be slid over first cylindrical portion including a second pair of opposing slots, the first and second cylindrical portions are loosely secured together by a clip fitted within the first and second pair of slots. The first electrical contact is received through a first one of the notches and secured about some of plurality of pins including a moveable spring portion. The second electrical contact is received through a second one of the notches and secured about others of the plurality pins and spaced from the spring portion. The pin is loosely received through the through bore, the first electrical contact lightly biasing the pin against the diaphragm, the pin moveable in response to the motion of the diaphragm in response to the pressure differential thereacross, the pin urging the first electrical contact away from the second electrical contact in response to the snap action of the diaphragm when a low pressure condition arises in the pressurized chamber.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.